Satellite antenna systems are often used to provide communications between mobile ground-based terminals. Reliable communications between terminals is preferable to all users however, some applications have an especially critical need for robust operation. Military applications, for example, require a system that maintains communication between highly mobile terminals even in the presence of jamming signals and other sources of interference. Although jamming will be discussed below, the invention is equally applicable to any source of interference in a communication signal, intentional or unintentional.
In a communication environment with large jamming sources in the same receive bandwidth as the desired signal from a terminal, communication performance will be degraded significantly if anti-jamming measures are not employed. Numerous techniques have been proposed for dealing with this type of problem. Nulling approaches (Howells-Applebaum, U.S. Pat. No. 5,175,558 and U.S. Pat. No. 6,130,643) all attempt to preserve an overall pattern performance to all possible users, across the full system bandwidth, in the presence of jammer signals. An antenna with a nuller uses beamforming to constructively add signals from a desired source such as a mobile terminal, and cancel out the signals from a jamming or other undesired source. These approaches, however, are suboptimal.
Instead of nulling an interference source across all users, another architecture for the jamming problem is to optimize performance for each terminal independently against the jammer. Several approaches exist for optimizing performance to each user independently, for example, by means of beamforming with optimal combining (OC) and maximum ratio combining (MRC). These approaches suffer from either poor performance in the presence of jamming or interference, or require some knowledge of user and/or jammer location to be effective as further described by B. R. Tomiuk and N. Beaulieu, “A New Look at Maximal Ratio Combining”, Global Telecommunications Conference, 2000, GLOBECOM'00 IEEE, vol. 2, pp. 943-948, November 2000. Without knowledge of the terminal/jammer locations, estimation techniques must be employed, however simple estimation techniques result in poor performance.
Thus, there exists a need for a satellite antenna system that combines optimized individual terminal beamforming with anti-jamming capabilities. There further exists a need for a method that optimizes for each user independently only over the user's receive bandwidth.